Potassium EDTA specimens are also acceptable.

Reference range:	Normal:	<15µmol/L
	Moderate hyperhomocysteinaemia:	16-30µmol/L
	Intermediate hyperhomocysteinaemia:	31-100µmol/L
	Severe hyperhomocysteinaemia:	>100µmol/L

Causes of an increased plasma homocysteine level	Causes of a decreased plasma homocysteine level
Analytical
Delayed sample separation can artificially increase homocysteine levels. Samples must be transported to the laboratory immediately and centrifuged within 1 hour.
Genetic factors
Homocystinuria, methylenetetrahydrofolate reductase (MTHFR) mutation 677C->T.	Down's Syndrome
Lifestyle determinanants
Smoking	Vitamin intake (folate, cobalamin, B6, B12), exercise.
Clinical conditions
Folate deficiency, cobalamin deficiency, renal failure, hypothyroidism, cardiovascular disease, cerebral vascular accident, thrombophilia
Drugs
Anti-folates (methotrexate, anticonvulsants, trimethaprim), nitrous oxide anesthesia, L-Dopa, fibrates, cyclosporin.
Physiological determinants
	Pregnancy

Other investigations to consider when plasma homocysteine levels are raised:

• Vitamin B₆ and B₁₂ measurement.
• Folate measurement.
• Methylenetetrahydrofolate reductase (MTHFR) genotyping^*.
• Methionine loading test^#.

# Used to reveal additional abnormalities of the homocysteine metabolism not detected by homocysteine concentration measurements. An elevated homocysteine level post methionine load must be taken into account in the general identification of patients bearing trans-sulphuration defects (e.g. vitamin B₆ deficiency) or heterozygotes for cystathionine β-synthase (CBS) deficiency. Please contact duty biochemist for further information.

Additional information on Homocysteine and its clinical use can be found here: Homocysteine.

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